Process for the continuous preparation of vinyl acetate

ABSTRACT

THE ACTIVITY AND SELECTIVITY OF CATALYSTS COMPRISING PALLADIUM META AND AN ALKALI METAL ACETATE, WHEN USED FOR THE PRODUCTION OF VINYL ACETATE FROM ETHYLENE, OXYGEN AND ACETIC ACID, IS MAINTAINED AT A HIGH LEVEL EVEN AFTER PROLONGED LONG TERM CONTINUOUS USED, BY THE CONTINUOUS ADDITION OF QUANTITIES OF ALKALI METAL ACETATE TO A REACTANT STREAM OR THE REACTION SPACE.

United States Patent Olfice 3,830,834 Patented Aug. 20, 1974 3,830,834PROCESS FOR THE CONTINUOUS PREPARATION OF VINYL ACETATE Walter Kronig,Wiesbaden; Gunter Roscher, Kelkheim; Wulf Schwerdtel, Cologne, and KurtSennewald, Huerth-Mitte, Germany, assignors to Bayer Aktiengesellschaftand Farbwerke Hoechst Aktiengesellschaft vormals Meister Lucius 8:Bruuing, Frankfurt am Main Hoechst, Germany No Drawing.Continuation-impart of abandoned application Ser. No. 682,564, Nov. 13,1967. This application Aug. 11, 1971, Ser. No. 170,967

Claims priority, application Germany, Nov. 12, 1966,

K 60,705; Dec. 27, 1966, F 51,091

Int. Cl. C07c 67/04 US. Cl. 260-497 A 23 Claims ABSTRACT OF THEDISCLOSURE The activity and selectivity of catalysts comprisingpalladium metal and an alkali metal acetate, when used for theproduction of vinyl acetate from ethylene, oxygen and acetic acid, ismaintained at a high level even after prolonged long term continuoususe, by the continuous addition of quantities of alkali metal acetate toa reactant stream or the reaction space.

This application is a continuation-in-part of SN. 682,564 filed Nov. 13,1967, and now abandoned.

The present invention relates to a new and eflicient catalytic processfor the preparation of vinyl acetate and, more particularly, to aprocess which permits long-term continuous production of vinyl acetate.

It is known from US. Pat. 3,275,680 that vinyl acetate can be preparedby reacting ethylene with acetic acid and oxygen at elevatedtemperatures in the presence of catalysts containing palladium metaland, advantageously, an alkali metal acetate. British Pat. 1,017,938discloses for the preparation of vinyl acetate in a gas-phase processthe use of a palladium catalyst which is pretreated with alkali metalacetate. In British Pat. 1,103,725 the production of vinyl acetate isdescribed using a catalyst as disclosed in US. Pat. 3,275,680 whichadditionally contains gold metal. These processes yield vinyl acetate ingood yield and, initially, with satisfactory space-time yields, but ithas been found that the space-time yield in this process does drop overtime and that the selectivity of the process to form vinyl acetate, asopposed to undesired by-products, also decreases over time.

Many attempts have been made in the art to solve this problem ofdiminishing yields and decreasing selectivity because, in commercial andpractical operation, it is essential to maintain high catalytic activityand selectivity over very extended periods of time of e.g., up to a yearand more.

The art, e.g., US. Pat. 3,480,558, ascribed this loss of catalystactivity experienced in prior art processes to factors such as lack ofcatalyst stability. This problem was sought to be solved by regeneratingthe catalyst after relatively short periods of use. However, theregenerating techniques disclosed in the art are cumbersome, multistepmethods which have not been found to be satisfactory. In addition, ofcourse, the process must be interrupted to remove and regenerate thecatalyst. Other factors that have been suggested as leading to loss ofcatalyst activity are a gradual poisoning of the catalyst due to anacumulation of by-products and/or inertsin the reaction system. It wasthought that deposits formed on the catalyst or a coating of thecatalyst gradually took place thereby diminishing the activity of thecatalyst. .Howe'ver, it was subsequently discovered that methods thateliminated or mitigated the accumulation of such foreign material didnot result in maintaining catalyst activity and selectivity. Thisinability of the prior art to overcome the deficiencies of the knownprocess thus indicated that foreign matter accumulation was not the realor determining factor in causing loss of catalyst life. Prior to theinstant invention, no satisfactory way had been found to maintaincatalyst activity at a very high level over prolonged periods whenmaking vinyl acetate from ethylene, oxygen and acetic acid.

-It has now been surprisingly found that catalyst activity andselectivity of a catalyst comprising palladium metal and alkali metalacetate in processes for making vinyl acetate, may be maintained at avery high level for very prolonged periods of operation of the process,e.g., for periods of up to one year or more.

Essentially, the process of this invention comprises continuouslyintroducing to a reactant stream or to the reaction space in which vinylacetate is formed amounts of alkali metal acetate, or of a compound thatforms an alkali metal acetate under the reaction conditions. The amountof alkali metal acetate or compounds so introduced is preferably such asto substantially saturate the reactant stream or the reaction space withgaseous alkali metal acetate or compound. Conveniently, the alkali metalacetate so introduced is the same as the alkali metal acetate used as acatalyst component.

The amount of alkali metal acetate so introduced depends on the specificreaction system and reaction conditions used but will generally be inthe range of 2 to 200 parts per million, and preferably from 5 to 50parts per million, based on the amount of acetic acid introduced intothe reactor. The amount is preferably such that the reaction system orreactant stream into which the acetate is introduced is substantiallyloaded with alkali metal acetate, i.e., wherein the stream or spaceholds substantially as much acetate as it can possibly hold. Thus,amounts corresponding to e.g., to of the saturation value which thealkali metal acetate in the reactor space has are desirably used. Whilethese amounts of alkali metal acetate or compound introduced are notlarge in an absolute sense they dramatically and surprisingly alter andimprove the efliciency and life-span of continuous processes for makingvinyl acetate.

The term alkali metal compounds which form alkali metal acetate is hereunderstood to mean any compound which is capable of forming alkali metalacetates under the reaction conditions; e.g., there can be mentionedalkali metal hydroxides, alkali metal carbonates, alkali metalboronates, alkali metal phosphates and alkali metal carboxylates. Suchcompounds are capable of forming alkali metal acetate in situ, in thepresence of the acetic acid reactant, in the reaction system, whenoperating the vinyl acetate process as taught by the art, i.e., at fromabout 50 to- 250 C. and at, e.g., normal to 200 atmospheres pressure(see U .S. Pat. 3,275,680, which generically discloses the process formaking vinyl acetate to which the instant invention is applicable).

The alkali metal acetate or compound may be added or introduced to thereactants in various manner: the alkali metal acetate or compound may,for example, be dissolved in the acetic acid reactant, e.g., dissolvedin the fresh acetic feed. Preferably, however, the alkali metal compoundor acetate is introduced into a reactant stream containing at leastethylene and acetic acid at a temperature where said ethylene and aceticacid are entirely in the gas phase. Preferably, the alkali metal acetateor alkali metal compound is introduced into the reactant gas streamcontaining primarily ethylene and acetic acid at conditions oftemperature and pressure being approximately similar to the conditionsof temperature and pressure in the reactor. It has, in one surprisingaspect of the invention, been found that an alkali metal acetate may beintroduced in entirely gaseous form when introducing it into anethylene/acetic acid gas mixture at temperatures above about 120 C. atnormal or elevated pressure. This effect is most surprising becausealkali metal acetate, and other alkali metal salts contemplated for usein this invention, are salts which would not be expected to volatilizeunder the conditions in which they are used in the instant invention.

The surprising volatilization of alkali metal acetate when introducedinto a gas mixture containing ethylene and acetic acid does not occurwhen it is attempted to volatilize such acetate in an ethylene streamcontaining no acetic acid (see Example 8, infra).

When so introducing the alkali metal acetate or compound to a reactantstream in the gas phase the alkali metal acetate or compound may bedissolved in a suitable solvent, for example, acetic acid or water, andthe resulting solution can be introduced, e.g., sprayed, into the streamof hot gas which ultimately enters the reactor. Both the solvent andsolute, i.e., the alkali metal acetate or compound, completely evaporateand exist totally in the gas phase in the hot gas reactant stream.

In another embodiment, the heated gaseous reactants may be conductedpartly or entirely at elevated temperature through a solution of thealkali metal salts, the hot gases carrying the alkali metal salts withthem and introducing them into the reaction chamber.

Furthermore, the alkali metal salts may be introduced into the reactantsby passing the reactants partly or entirely in the gaseous form atelevated temperature through an alkali metal cartridge, e.g., a layer ofsolid bodies which are impregnated with the alkali metal salts. Suitablesolid bodies include, for example, porous materials which are notattacked by the reactants under the operating conditions. Silicic acid,for example, may be used as a carrier. The concentration of alkali metalcompounds in the carriers may be about 1% to 20% by weight. The streamof gas may be passed upwards, or downwards, or horizontally through thelayer of solid material. The temperature in the layer of solid materialis preferably chosen to be near the reaction temperature, but may, ifdesired, be slightly above or slightly below this. The apparatuscontaining the solid bodies is also kept at the same pressure as thereaction chamber. If the solid bodies have become impoverished in alkalimetal salts after a certain period of operation, the process may betransferred to another assembly filled with freshly impregnated solidbodies. Alternatively, the alkali metal compounds may be supplied insolution continuously or intermittently to the layer of solid bodies,thereby maintaining the solid layer sufficiently charged with alkalimetal salts.

With respect to the catalyst to which the instant invention isapplicable, palladium, which may contain additions of metal such as goldas well as other noble metals of Group VIII of the Periodic System, suchas iridium, ruthenium, platinum, rhodium and osmium, is especiallysuitable as a catalyst for the reaction. It is preferable to employcarrier catalysts. Suitable concentration of the noble metals on thecarrier are from 0.05 to 5 grams, preferably from 0.1 to 2 grams, of thenoble metals per 100 cc. of the catalyst charge. The additives to thepalladium may be used in quantities of, for example, from 2 to 150 partsby weight of palladium. Porous materials which are not attacked by thereactants under the reaction conditions, are suitable for use ascarriers for the noble metals. Examples of porous materials which are.

suitable for this purpose are silicic acid, silicates such as magnesiumsilicate and aluminum silicate, kieselguhr, annealed aluminum oxide,spindels, silicone carbide, aluminum phosphate, asbestos, pumice andactive charcoal. The alkali metal salts are then applied to the carriersprovided with the noble metals.

The carrier materials should generally have an active surface areabetween about 50 and 400 mF/g. The catalyst carrier used for preferenceis silicic acid which has an active surface area according to BET of,for example, 50 to 200 m. /g., e.g., 180 m. /g., and a bulk density of,for example, 0.5 kg./l.

The catalyst, which may, for example, be fixed in the reaction chamber,should contain from 0.1% to 10%, and preferably from 1% to 5% by weight(based on the catalyst carrier) of alkali metal salts. In principle, anyalkali metals may be used; but lithium, sodium and potassium, andmixtures of these alkali metals are especially suitable. The alkalimetals are generally introduced as acetates, but the alkali metals mayalso be applied in some other form to the catalyst, e.g., as hydroxides,carbonates, borates, phosphates and carboxylates.

The noble metals are preferably applied to the carriers in form of theirsalts and the salts are reduced with suitable agents to the metals, forexample with hydrazine, sodium formate, hydrogen-containing gases,methanol vapors, ethylene, etc. The anions introduced with the noblemetal salts can be removed for example by washing if necessary.

The reaction of ethylene with acetic acid and oxygen is carried out inthe gaseous phase at elevated temperature, e.g., at temperatures between50 C. and 350 C., preferably 100 C. to 250 C. The pressure employed maybe normal pressure, slightly reduced or elevated pressure, e.g. up toabout 200 atmospheres, preferably up to 20 atmospheres. The molar ratioof ethylene to oxygen may, for example, be between :20 to 98:2, and themolar ration of acetic acid to ethylene may be between 1:1 to 1:100. Thehourly throughput of ethylene through 1 liter of reaction space isadvantageously between 5 and 50 mols.

It has proved to be advantageous to subdivide the reaction chamber intoseveral parallel tubes which are surrounded on the outside by a coolingliquid, preferably an evaporating liquid such as water.

The internal width of the tubes should be between 30 and 60 mm. and thelength between 1 and 20 m.; it is advantageous to adjust the length sothat the flow velocities obtained, based on the empty reaction chamber,are between 10 and 200 cm. per second.

The invention is further illustrated by the following examples withoutbeing restricted there-to.

EXAMPLE 1 (a) The reaction chamber, consisting of a pipe of 20 mm.internal width and 1500 mm. length surrounded by hot water, was filledwith 1 liter of catalyst which contained 18 g. of palladium and 20 g. ofsodium acetate on a lithiu-m/ aluminum spinel carrier. A mixtureconsisting of 9.10 gram mols of ethylene, 3.50 g. mols of acetic acidand 1165 g. mols of oxygen was passed hourly in a downward stream at 140C. and at atmospheric pressure over 1 liter of this catalyst. Thereact-ants were then converted in the reaction chamber into vinylacetate and water with the formation of small quantities ofcarbondioxide as a lay-product. The Table given below shows the outputof vinyl acetate based on grams of vinyl acetate per liter of reactionchamber and per hour, and the selectivity of formation of vinyl acetatein terms of the molar ration of vinyl acetate formed based on convertedethylene. The remainder to make up 100 consists mainly of carbondioxide.

(b) In the comparison test, the same conditions were employed 'but 12mg. of sodium acetate dissolved in 20 g. of acetic acid were sprayedevery 6 hours into the reaction chamber onto the catalyst. The outputand selectivity obtained are shown in Table 1. It will be seen thatdecrease of cat-alyst activity was prevented by the addition of sodiumacetate.

EXAMPLE 2' (COMPARISON EXAMPLE WITH- OUT ALKALI MiETAL ACETATE) 1 kg. ofa silicic acid carrier in the form of spherical pellets of 4 mm.diameter was mixed and thoroughly impregnated with an aqueous solutioncontaining 8 g. of Pd as Pd'Cl and 3 g. of Au as H[AuCl The mixture wasthen dried with stirring to achieve uniform distribution of the noblemetal salts on the carrier, and the dry mass was slowly introduced intoa 4-5% hydrazine hydrate solution at 40 C. After reduction of the noblemetal compound was complete, the supernatant liquid was poured off, andthe catalyst was thoroughly washed with distilled water and dried undervacuum at 60 C. The catalyst prepared in this way contains about 0.8% ofPd and0.3% of Au and has a bulk density of 0.54 kg. per liter.

350 cc. of the catalyst mass were introduced into a tube of 18/8 chromenickel steel of 25 mm. internal diameter inside which was a central tubeof thesame material of 14 mm. external diameter designed to containthermocouples for the temperature measurement, and the catalyst was keptat 170 C. by tempering the tube. A gaseous mixture consisting of 100 Nliters of ethylene, 70 N liters of air and 160 g. of acetic acid Waspassed hourly through the vertical tube at a pressure of 6 atmospheres.The condensable constituents were removed by condensation from thegaseous mixture leaving the reaction tube by cooling to 70 C., andanalysed by distillation or gas chromatographic analysis. The volume/time yields were only 10 to 20 g. of vinyl acetate per liter of contactper hour.

EXAMPLE 3 (COMPARISON EXAMPLE WITH SODIUM ACETATE) 350 cc. of thecatalyst prepared as in Example 2 were impregnated with 350 cc. of a 10%aqueous sodium acetate solution, the supernatant liquid was decanted,and the mixture was then dried under vacuum at 60 C. This catalystcontained 0.76% Pd, 0.28% An and 1.5% Na as sodium acetate. Outputs ofup to 94 g. of vinyl acetate per liter of catalyst per hour wereobtained with this catalyst under same conditions as in Example 2. Thecatalyst output dropped to 46 g. of vinyl acetate per liter of catalystper hour within 19 days. During this time, 1.1 g. of Na, or about 40% ofthe sodium acetate originally present, had migrated from the carriercatalyst while the average content in the condensate was p.p.m. of Na.After removal of the catalyst, outputs of up to 70 g. of vinyl acetateper liter of catalyst per hour can be obtained by adjusting the sodiumcontent to the original value simply by impregnating the catalyst withsodium acetate solution again.

EXAMPLE 4 (COMPARISON EXAMPLE WITH POTASSIUM ACETATE) A catalystprepared as in Example 2 was charged with 4.2% K by impregnating it witha 15% potassium acetate solution. Under the conditions indicated inExample 2, outputs of 140 g. of vinyl acetate per liter of catalyst perhour were obtained with this catalyst. After an operating time of 55days, the catalyst output was still at 120 g. of vinyl acetate per literof catalyst per hour. During this time, 1.5 g. of potassium in the formof the acetate had migrated from the catalyst with the condensate,corresponding to about 19% of the potassium acetate originally present.This clearly showed a substantial increase in catalyst life over thatobtained in the experiment described in Example 3, owing to the reducedrate of migration of potassium acetate compared with sodium acetate.

EXAMPLE 5 (COMPARISON EXAMPLE WIT'H POTASSIUM AC'ETATE/CA-ESIUM ACETATE)Using a catalyst which was similar except for containing 3% potassiumand 2.5% caesium as acetates, outputs of 140 to 150 g. of vinyl acetateper liter of catalyst per hour were obtained under the reactionconditions of Example 2. No loss in output could be detected after anoperating time of 40 days. During this time, 0.35 g. of caesium,corresponding to about 8% of the caesium originally present, and 1.23 g.of potassium (22% of the potassium originally present) were dischargedas acetates with the reaction gases.

EMMPLE 6 (ACCORDING TO THE INVENTION) Under the reaction conditions ofExample 2, a catalyst which contained 0.62% Pd, 0.25% Au, 1.4% Na and2.5 K on silicic acid as a carrier reached a space-time yield after adevelopment period of 135 g. of vinyl acetate per liter of catalyst perhour, which, in the course of a further 7 days, dropped to g. of vinylacetate per liter of catalyst per hour. Within this period, the alkalimetal acetate contents in the condensate due to migration of the alkalimetal acetate were at about 15 p.p.m. Na and about 7 p.p.m. K. The samequantity of alkali metal acetate (15 p.p.m. Na and 7 p.p.m. K) as foundin the condensate was now supplied with the acetic acid to the aceticacid evaporator heated to 190 C. The space-time yield thereupon risesagain to g. of vinyl acetate per liter of catalyst per hour in thecourse of a further 14 days.

EXAMPLE 7 (ACCORDING TO THE INVENTION) 690 N liters of ethylene, 480 Nliters of air and 1400 g. of acetic acid were conducted per hour underthe conditions of Example 2 over 2.4 liters of a catalyst containing0.7% Pd, 0.27% Au, 1.5% Na as CH COONa and 3.3% as CH COOK on silicicacid as a carrier. Space-time yields on an average of to g. of vinylacetate per liter of catalyst per hour had become established on thesecond day and remained constant over a period of 45 days. After afurther 10 days, the catalyst output dropped, owing to loss of alkalimetal acetate from the catalyst, to 80 g. of vinyl acetate per liter ofcatalyst per hour. Up to that time, the entire sodium acetate and about35% of the potassium acetate originally present on the catalyst had beendischarged with the reaction gases. A cartridge of 100 g. of catalystcarrier (silicic acid) containing 2.7% Na and 4.9% K in the form of theacetates was now installed in the stream of starting gases in front ofthe reactor to replenish the catalyst with alkali metal acetates andboth cartridge and reaction tube were heated to C. About 95% of thesodium acetate and 70% of the potassium acetate migrated from thecartridge into the catalyst in the course of 14 days. Replenishment ofthe catalyst with alkali metal acetate was repeated by renewing thealkali metal acetate cartridge. By this measure, the catalyst outputagain rose on the 60th day to 135 g. of vinyl acetate per liter ofcatalyst per hour and remained unchanged over a further period of 35days.

The surprising effect of volatilization of alkali metal acetate added toa hot reactant gas stream containing acetic acid was demonstrated by thefollowing Example.

EXAMPLE 8 Experiment A 1000 milliliter of a porous inert supportconsisting of aluminum oxide with an inner surface of 1 m. g. wereimpregnated with an aqueous sodium acetate solution in such a mannerthat one liter of the support contained 30 grams of sodium acetate. 650milliliters of this impreg- Experiment B Experiment A was repeated witha different amount of ethylene, as set forth in Table 1.

Experiment C Experiment A was repeated except that, instead of ethylenealone, a mixture of ethylene and acetic acid was passed over freshsupport in the manner described in Experiment A, at the rates stated inTable 1. The gas leaving the tube was analyzed as in Experiment A. Theresults are set forth in Table 1.

TAB LE 1 Gas rate in moles/hour Mole per- Mole-ppm) cent acetic sodiumEthyl- Acetic acid in acetate Experiment ene acid Total gas in gas A. 404o 0 1 B 50 0 50 0 1 G 40 10 50 20 35 *1 m0le-p.p.m.=0.000l molepercent.

The above experiments A, B and C demonstrate that the sodium acetate isnot volatilized if only ethylene gas is conducted over the supportcontaining sodium acetate. If however, an ethylene/ acetic acid gasstream is used, the sodium acetate volatilizes so that the resulting gasstream contains gaseous sodium acetate.

While applicants do not rely on any particular theory for the success oftheir invention, their experiments have shownthat a mere mechanicaladdition of alkali metal acetate or compound to a catalyst which hasbeen used for extended periods, e.g., one month or so, and has therebybecome greatly less elfective, does not restore catalytic activity tothe level achieved by fresh catalyst. Contrariwise, proceeding inaccordance with this invention, results in maintaining catalyticactivity at substantially freshcatalyst levels. Accordingly, it isevident that effects other than mechanical replenishment of the alkalimetal acetate are involved in the instant invention.

It will be understood that the foregoing specification and examples areillustrative and not limitative of the present invention in that manyother embodiments of the invention will suggest themselves to thoseskilled in the art.

What is claimed is:

1. In a process for the continuous production of vinyl acetate byreacting ethylene with acetic acid and oxygen in the gas phase atelevated temperature in a reactor in the presence of a catalystconsisting essentially of palladium metal and an alkali metal acetate,and optionally a noble metal selected from the group consisting of gold,iridium, ruthenium, platinum, rhodium and osmium, the improvement whichcomprises introducing into a gaseous reactant stream containing aceticacid or into the reactor gaseous alkali metal acetate or a compoundforming gaseous alkali metal acetate under the reaction conditions, inamount sufficient to prolong catalyst life.

2. Improvement as claimed in claim 1 wherein said alkali metal acetateor compound is introduced in amount of from 2 to 200 parts per million,by weight, based on the acetic acid introduced into the reactor.

3. Improvement as claimed in claim 2 wherein said amount is 5 to 50parts per million, by weight.

4. Improvement as claimed in claim 1 wherein said alkali metal acetateor compound is introduced in amounts corresponding to 80 to 100% of thesaturation value of the alkali metal acetate in the reactor space.

5. Improvement as claimed in claim 1 wherein said alkali metal acetateor compound is sodium acetate.

6. Improvement as claimed in claim 1 wherein said alkali metal acetateor compound is potassium acetate.

7. Improvement as claimed in claim 1 wherein said elevated temperatureis from about 50 to about 250 C. 5 8. Improvement as claimed in claim 7wherein the reaction pressure is from about normal pressure to about 200atmospheres (gauge).

9. Improvement as claimed in claim 1 wherein said catalyst contains goldas said noble metal. 10 10. Improvement as claimed in claim 1 whereinsaid catalyst consists of palladium metal, gold metal and sodium acetateand the introduced alkali metal acetate 01 compound is sodium acetate.

11. Improvement as claimed in claim 1 wherein said catalyst consists ofpalladium metal, gold metal and potassium acetate, and the introducedalkali metal acetate or compound is potassium acetate.

12. Improvement as claimed in claim 1 wherein said alkali metal acetateor compound is introduced to an ethylene gas stream containing aceticacid.

13. Improvement as claimed in claim 1 wherein said alkali metal acetateor compound is introduced into a reactant gas stream containingprimarily ethylene and acetic acid at conditions of temperature andpressure substantially the same as the conditions of temperature andpressure in the reactor.

14. Improvement as claimed in claim 13 wherein said acetic acid/ethylenegas stream is at a temperature above about 120 C.

15. Improvement as claimed in claim 14 wherein the acetic acid/ethylenegas stream is at a pressure of from 1 to 8 atmospheres (gauge).

16. Improvement as claimed in claim 1 wherein said introduced alkalimetal acetate or compound is introduced by dissolving it in liquidacetic acid and then vaporizing the resulting solution.

17. Improvement as claimed in claim 1 wherein said alkali metal acetateor compound is introduced into the reaction space. 40 18. Improvement asclaimed in claim 1 wherein said introduced alkali metal acetate orcompound is introduced by passing a reactant stream through a solutionof the alkali metal acetate or compound, in the presence of acetic acid.

19. Improvement as claimed in claim 18 wherein the alkali metal acetateor compound is introduced in the form of an aqueous or acetic acidsolution.

20. Improvement as claimed in claim 1 wherein said catalyst is on acarrier support.

21. Improvement as claimed in claim 20 wherein said carrier support issilicic acid or a silicate.

22. Improvement as claimed in claim 1 wherein said introduced alkalimetal acetate or compound is introduced by passing at least one of thereactants at an elevated temperature through a layer of solid bodies,impregnated with said alkali metal acetate or compound, in the presenceof acetic acid.

23. Improvement as claimed in claim 1 wherein said process is a longterm continuous process operated con- 60 tinuously for a period ofgreater than 6 months.

References Cited UNITED STATES PATENTS LORRAINE A. WEINBERGER, PrimaryExaminer R. D. KELLY, Assistant Examiner U.S. Cl. X.R.

